1. FIELD OF THE INVENTION
This invention relates to a power unit for hydraulic elevators and, more particularly, to a hydraulic elevator power unit in which an electric motor and a hydraulic pump driven by this electric motor are submerged in an operating oil contained in an oil reservoir.
2. DESCRIPTION OF THE RELATED ART
A submerged type power unit such as the ones disclosed in Japanese Patent Laid-Open Nos. 62-275986 and 64-34881 are known in which an electric motor and a hydraulic pump are submerged in an operating oil in an oil reservoir. In this type of power unit, a detector for detecting the number of revolutions of the electric motor is also submerged in the operating oil. FIG. 1 is a schematic sectional side view of a conventional hydraulic elevator power unit. As shown in FIG. 1, an electric motor 3, a hydraulic pump 4 and a detector 10 connected to an end of the shaft of the electric motor 3 are submerged in an operating oil 2 contained in an oil reservoir 1. A hydraulic valve 6 disposed outside the oil reservoir 1 is connected to the hydraulic pump 4 by a discharge pipe 5, and a hydraulic jack 7 is connected to the hydraulic valve 6 by a piping 8. A cage 9 of the elevator is connected to the hydraulic jack 7.
The thus-constructed power unit is operated as described below. For upward movement of the cage 9, the operating oil 2 is supplied to the hydraulic jack 7 through the hydraulic valve 6 by the hydraulic pump 4, thereby moving the cage 9 upward. For downward movement of the cage 9, the operating oil 2 is made to return to the interior of the oil reservoir 1 through the hydraulic valve 6 and the hydraulic pump 4, thereby moving the cage 9 downward.
The cage traveling control is performed by detecting the number of revolutions of the electric motor 3 with the detector 10.
In this conventional hydraulic elevator power unit, an oil seal or an 0 ring is used to prevent the operating oil from entering the detector, since the detector is submerged in the operating oil. However, a very small amount of operating oil enters the detector through the oil seal and so on as the electric motor shaft is rotated. If the amount of entering oil becomes substantially large, there is a risk of the detecting portion being immersed in the operating oil and, hence, a risk of malfunction of the detector